I am sure there are plenty of good non-Monster cable makers out there, and I would never tell anyone they are the end all be all of cables. But...
At the risk of drawing a lot of negative comments, years ago I replace an "el cheapo" one with a 3' Monster Cable. As stated above, the shorter the cable the better. The Monster made a significant difference in terms of sound quality -- overall, the tone was cleaner (even when fully driven) and sounds better overall. That was almost 6 years ago, and I have never had a problem since.
No matter what brand of cable you decide on, it's probably worth spending a little bit of money now for better tone and longevity, at least in my opinoin.